During drilling operations, determining characteristics (such as the porosity) of the subsurface formation enables the locating and extracting of hydrocarbons to be more efficient and more profitable. One technique to determine these characteristics is to use radiation sources (such as pulsed neutron generators) downhole. The radiation sources output radiation into the subsurface formation. The resulting energy spectrum is monitored to determine the characteristics of the formation. The operation of these radiation sources in the presence of personnel can adversely affect the health of such personnel. Accordingly, a number of safety regulations for drilling operations require that such tools not be operational within a given distance of personnel.